A minor side reaction that produces VH+ and eliminates B3CH3 is also operative.
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Methane can not be obtained by this method. This type of reaction fails in case of tertiary halides. Also, since the reaction involves free radical species, a side reaction occurs to produce an alkene. This side reaction becomes more significant when the alkyl halides are bulky at the halogen-attached carbon atom.
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B and C from the above equations usually represent different compounds. However, they could also just be different positions in the same molecule. A side reaction is also referred to as competing reaction when different compounds (B, C) compete for another reactant (A). If the side reaction occurs about as often as the main reaction, it is spoken of parallel reactions (especially in the kinetics, see below).
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In many cases, self- condensation is an unwanted side-reaction. Therefore, chemists have adopted many ways to prevent this from occurring when performing a crossed aldol reaction.
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A side reaction is an unwanted chemical reaction taking place which reduces the yield of the desired product. The word synthesis was first used by the chemist Hermann Kolbe.
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Metalation of terminal alkynes is a significant side reaction that occurs under these conditions. If metalation is desired, tertiary amine complexes of DIBAL-H are useful.Binger, P. Angew. Chem. Int.
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Side reactions are also described in the reaction kinetics, a branch of physical chemistry. Side reactions are understood as complex reaction, since the overall reaction (main reaction + side reaction) is composed of several (at least two) elementary reactions. Other complex reactions are competing reactions, parallel reactions, consecutive reactions, chain reactions, reversible reactions, etc. [10] If one reaction occurs much faster than the other one (k1 > k2), it (k1) will be called the main reaction, the other one (k2) side reaction.
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In some cases, the use of triethylamine as the base can lead to epimerisation at the carbon alpha the newly formed carbonyl. Using a bulkier base, such as diisopropylethylamine, can mitigate this side reaction.
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When heated, ammonium formate eliminates water, forming formamide. Upon further heating, it forms hydrogen cyanide (HCN) and water. A side reaction of this is the decomposition of formamide to carbon monoxide (CO) and ammonia.
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The water-gas shift reaction may be an undesired side reaction in processes involving water and carbon monoxide, e.g. the rhodium-based Monsanto process. The iridium-based Cativa process uses less water, which suppresses this reaction.
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A significant undesired side reaction which occurs during the baking process produces aromatic polyamines. Urethane crosslinkers based on toluene diisocyanate (TDI) can be expected to produce toluene diamine as a side reaction, whereas those based on methylene diphenyl diisocyanate produce diaminodiphenylmethane and higher order aromatic polyamines. The undesired aromatic polyamines can inhibit the cure of subsequent acid catalysed topcoat layers, and can cause delamination of the subsequent topcoat layers after exposure to sunlight. Although the industry has never acknowledged this problem, many of these undesired aromatic polyamines are known or suspected carcinogens.
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The dimerization reaction 2SF2 FSSF3 is reversible. It also disproportionates: SF2 \+ FSSF3 → FSSF + SF4. A side reaction also produces the intermediate F3SSSF3. hydrogen fluoride catalyses disproportionation to sulfur and sulfur tetrafluoride by forming a reactive intermediate HSF molecule.
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Inevitably, [4+4] photocycloadditions carry the side reaction of [2+2] photocycloadditions. However, since these reactions are reversible, the most stable product may be formed through thermodynamic control. A 4+4 cycloaddition occurring over two 2+2 cycloaddition steps.
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The capacity of these types of substituents to leave is sometimes exploited synthetically, particularly the case of replacement of silyl by another functional group (ipso attack). However, the loss of groups like iodo or alkyl is more often an undesired side reaction. :Reaktion mechanism for elektrophilic aromatic substitution.
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The chelator can have an effect on the kinetic rate and even the catalyzed reaction. If the substrate Mn(II) is chelated with lactate, MnP instead catalyzes the evolution of O2. However, this side reaction has little impact on enzymatic activity because it follows slower third order kinetics.
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As previously done for DAMA/NaI, careful investigations on absence of any significant systematics or side reaction in DAMA/LIBRA have been quantitatively carried out. The obtained model independent evidence is compatible with a wide set of scenarios regarding the nature of the dark matter candidate and related astrophysical and particle physics.
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Medrogestone synthesis. Reduction of the conjugated 16,17 double bond of 6-methyl-16-dehydropregnenolone acetate by means of lithium in liquid ammonia leads initially to the 17 enolate ion; this is alkylated in situ with methyl iodide. The now-familiar steric control asserts itself to afford the 17α-methyl compound,. The acetate group is lost as a side reaction.
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Step 1 details the oxidation of ammonia into nitrite via ammonia-oxidizing bacteria. The most frequent genus of bacteria identified as being the facilitator of this step is Nitrosomonas. These bacteria will produce small quantities of nitrous oxide from produced nitrite in a side reaction. Nitrous oxide emissions increase as soil pH concentration increases or becomes more basic.
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Organocuprates may also be employed for the reduction of α,α'-dihalo ketones to alkylated ketones. In the absence of an electrophile the monoalkyl ketone is isolated in good yield;Posner, H. ; Sterling, J J. Am. Chem. Soc. 1973, 95, 3076. when an alkyl iodide is added, the dialkyl ketone is isolated (geminal alkylation is a problematic side reaction).
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Wanzlick equilibrium Carbenes and carbenoid precursors can undergo dimerization reactions to form alkenes. While this is often an unwanted side reaction, it can be employed as a synthetic tool and a direct metal carbene dimerization has been used in the synthesis of polyalkynylethenes. Persistent carbenes exist in equilibrium with their respective dimers. This is known as the Wanzlick equilibrium.
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About five percent of hydrogen gas produced worldwide is created by electrolysis. Currently, most industrial methods produce hydrogen from natural gas instead, in the steam reforming process. The majority of the hydrogen produced through electrolysis is a side product in the production of chlorine and caustic soda. This is a prime example of a competing for side reaction.
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Many metathesis reactions with ruthenium catalysts are hampered by unwanted isomerization of the newly formed double bond, and it is believed that ruthenium hydrides that form as a side reaction are responsible. In one study Hong, S. H.; Sanders, D. P.; Lee, C. W.; Grubbs, R. H. (2005). "Prevention of Undesirable Isomerization during Olefin Metathesis". J. Am. Chem. Soc. 127 (49): 17160–17161. . .
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A commonly encountered side-reaction in Wolff–Kishner reductions involves azine formation by reaction of hydrazone with the carbonyl compound. Formation of the ketone can be suppressed by vigorous exclusion of water during the reaction. Several of the presented procedures require isolation of the hydrazone compound prior to reduction. This can be complicated by further transformation of the product hydrazone to the corresponding hydrazine during product purification.
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Norsorex or polynorbornene is another important ROMP product on the market. Telene and Metton are polydicyclopentadiene products produced in a side reaction of the polymerization of norbornene. The ROMP process is useful because a regular polymer with a regular amount of double bonds is formed. The resulting product can be subjected to partial or total hydrogenation, or can be functionalized into more complex compounds.
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They react to produce phosphinates. Heating is also required for the reaction, but pyrolysis of the ester to an acid is a common side reaction. The poor availability of substituted phosphonites limits the usage of this class of reagent in the Arbuzov reaction. Hydroxy, thiol, carboxylic acid, primary and secondary amine functional groups cannot be used with phosphonites in the reaction as they all react with the phosphonite.
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Dowd–Beckwith reaction A side reaction accompanying this ring expansion is organic reduction of the halo alkane to a saturated alkyl group. One study shows that the success depends critically on the accessibility of the carbonyl group. Deuterium experiments also show the presence of a 1,5 hydride shift. The reaction of the alkyl radical with the ester carbonyl group is also a possibility but has an unfavorable activation energy.
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Unfortunately, DBFCs do produce some hydrogen from a side reaction of NaBH4 with water heated by the fuel cell. This hydrogen can either be piped out to the exhaust or piped to a conventional hydrogen fuel cell. Either fuel cell will produce water, and the water can be recycled to allow for higher concentrations of NaBH4. More importantly, the process of creating electricity via a DBFC is not easily reversible.
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Primary amines are usually not used for enamine synthesis due to the preferential formation of the more thermodynamically stable imine species. Methyl ketone self-condensation is a side-reaction which can be avoided through the addition of TiCl4 into the reaction mixture (to act as a water scavenger). An example of an aldehyde reacting with a secondary amine to form an enamine via a carbinolamine intermediate is shown below: Enamine synthesis with a carbinolamine intermediate.
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Dimerization is a side reaction that can occur. When heated in xylene and sodium amide at atmospheric pressure, the substrate 4-tert-butylpyridine produces 89% of the dimer product (4,4'-di- tert-butyl-2,2'-bipyridine) and only 11% of the aminated Chichibabin product (2-amino-4-tert-butylpyridine). When subjected to 350 psi nitrogen pressure and the same conditions, the yields are 74% of the aminated Chichibabin product and 26% of the dimer product.
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The second principal side reaction is the reduction of the ketone or aldehyde to the corresponding alcohol. After initial hydrolysis of the hydrazone, the free carbonyl derivative is reduced by alkoxide to the carbinol. In 1924, Eisenlohr reported that substantial amounts of hydroxydecalin were observed during the attempted Wolff–Kishner reduction of trans-β-decalone. In general, alcohol formation may be repressed by exclusion of water or by addition of excess hydrazine.
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Nitrate is reduced to nitrite by nitrate reductase, while NO is mainly formed due to anaerobic reduction of nitrite which may take place in mitochondria by complex III and complex IV in the absence of oxygen, in the side reaction of nitrate reductase, or by electron transport proteins on the plasma membrane. The overall reaction sequence of the cycle consumes NADH and can contribute to the maintenance of ATP level in highly hypoxic conditions.
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The Perkow reaction is an organic reaction in which a trialkyl phosphite ester reacts with a haloketone to form a dialkyl vinyl phosphate and an alkyl halide. The Perkow reaction In the related Michaelis–Arbuzov reaction the same reactants are known to form a beta-keto phosphonate which is an important reagent in the Horner–Wadsworth–Emmons reaction on the road to alkenes. The Perkow reaction, in this respect is considered a side-reaction.
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The Neber rearrangement is an organic reaction in which a ketoxime is converted into an alpha-aminoketone via a rearrangement reaction. :Neber rearrangement The oxime is first converted to an O-sulfonate, for example a tosylate by reaction with tosyl chloride. Added base forms a carbanion which displaces the tosylate group in a nucleophilic displacement to an azirine and added water subsequently hydrolyses it to the aminoketone. The Beckmann rearrangement is a side reaction.
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The ketene formation during the deprotonation process for substrates possessing Evans' oxazolidinone is also a main side reaction for the related alkylation reactions. Development in the field of enamine chemistry and the utilization of imine derivatives of enolates managed to provide an alternative for enolate alkylation reactions. In 1963, G. Stork reported the first enamine alkylation reaction for ketones - Stork enamine alkylation reaction. A specific Stork enamine alkylation reaction between cyclohexanone and an electrophile.
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Hydrochloric acid generated during the selanylation of transient enol catalyzes tautomerization. (8)File:SelenScope5.png The seleno-Pummerer reaction is a significant side reaction that may occur under conditions when acid is present. Protonation of the selenoxide intermediate, followed by elimination of hydroxide and hydrolysis, leads to α-dicarbonyl compounds. The reaction is not a problem for more electron-rich carbonyls—generally, fewer side reactions are observed in eliminations of esters and amides. (9)File:SelenScope6.
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A side reaction is a chemical reaction that occurs at the same time as the actual main reaction, but to a lesser extent. It leads to the formation of by- product, so that the yield of main product is reduced: :{A} + B ->[{k_1}] P1 :{A} + C ->[{k_2}] P2 P1 is the main product if k1> k2. The by-product P2 is generally undesirable and must be separated from the actual main product (usually in a costly process).
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The Stetter reaction produces classically difficult to access 1,4-dicarbonyl compounds and related derivatives. The traditional Stetter reaction is quite versatile, working on a wide variety of substrates. Aromatic aldehydes, heteroaromatic aldehydes, and benzoins can all be used as acyl anion precursors with thiazolium salt and cyanide catalysts. However, aliphatic aldehydes can only be utilized if a thiazolium salt is used as a catalyst, as they undergo aldol condensation side reaction when a cyanide catalyst is used.
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Chain transfer is a polymerization reaction by which the activity of a growing polymer chain is transferred to another molecule.Flory, P. J. Principles of Polymer Chemistry, Cornell University Press, Ithaca, NY, 1953, p. 136. :P• + XR' → PX + R'• Chain transfer reactions reduce the average molecular weight of the final polymer. Chain transfer can be either introduced deliberately into a polymerization (by use of a chain transfer agent) or it may be an unavoidable side-reaction with various components of the polymerization.
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Schwartz's reagent can be used for a number of reactions. It has been shown that it can be used to reduce amides to aldehydes. Reducing tertiary amides with Schwartz's reagent can reach efficient yields, but primary and secondary amides will show decreased yields. The use of Schwartz's reagent in this manner will not require any added heat and can be done quickly, and reduction of the alcohol form is not a problematic side reaction as it can be with other reducing agents.
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Simple protodeboronation scheme Protodeboronation, or protodeborylation is a chemical reaction involving the protonolysis of a boronic acid (or other organoborane compound) in which a carbon-boron bond is broken and replaced with a carbon-hydrogen bond. Protodeboronation is a well-known undesired side reaction, and frequently associated with metal-catalysed coupling reactions that utilise boronic acids (see Suzuki reaction).Boronic Acids: Preparation and Applications in Organic Synthesis, Medicine and Materials, 2nd ed.; Hall, D., Ed; Wiley VCH: Weinheim, Germany, 2011; Vols.
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Methanethiol (MeSH) is released as a by-product of kraft pulping in pulp mills. In kraft pulping, lignin is depolymerized by nucleophilic attack with the strongly nucleophilic hydrosulfide ion (HS−) in a highly alkaline medium. However, in a side reaction, HS− attacks methoxyl groups (OMe) in lignin, demethylating them to give free phenolate groups (PhO−) and releasing MeSH. Due to alkalinity, MeSH is readily deprotonated (MeSNa), and the formed MeS− ion is also a strong nucleophile, reacting further to dimethyl sulfide.
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Enzyme promiscuity is the ability of an enzyme to catalyse a fortuitous side reaction in addition to its main reaction. Although enzymes are remarkably specific catalysts, they can often perform side reactions in addition to their main, native catalytic activity. These promiscuous activities are usually slow relative to the main activity and are under neutral selection. Despite ordinarily being physiologically irrelevant, under new selective pressures these activities may confer a fitness benefit therefore prompting the evolution of the formerly promiscuous activity to become the new main activity.
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This may also promote the full oxidation side reaction resulting in an increased CO2 concentration in the syngas. Additional equipment for gas cleanup including scrubber, catalytic steam reformer and/or tar reformer may be necessary downstream of the CLG system in order to remove or convert the unwanted byproducts in the syngas stream. Char, the remaining solid from the devolatilization and reactions, requires additional time for conversion. For a fluidized bed reducer with particle back mixing, unconverted char may leave the reducer with the reduced metal oxide particles.
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The formation of the corresponding carboxylic acid is a side reaction. When the alkyl group is an aliphatic chain (n typically 0 to 5), multiple reactions take place with the amide group always ending up at the terminal end. General scheme for the Willgerodt rearrangement An example with modified reagents (sulfur, concentrated ammonium hydroxide and pyridine) is the conversion of acetophenone to 2-phenylacetamide and phenylacetic acidThe Willgerodt Reaction. II. A Study of Reaction Conditions with Acetophenone and Other KetonesDeLos F. DeTar and Marvin Carmack J. Am. Chem. Soc.
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These additions have been rendered enantioselective through the use of chiral auxiliaries (see above) and chiral catalysts. Although the enantioselectivity of the proline-catalyzed process is good, yields are low and reaction times are long. :File:EAScope2.png Upon treatment with sulfonyl azides, a variety of Grignard reagents or enolates may be converted into azides or amines. A significant side reaction that occurs under these conditions is the diazo transfer reaction: instead of fragmenting into an azide and sulfinic acid, the intermediate triazene salt may break down to a diazo compound and sulfonamide.
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However, compared with other highly toxic nerve agents like soman or sarin, VX undergoes relatively slow "aging". Aging is a time-dependent side reaction (loss of an alkoxyl group) that occurs on nerve agents after phosphonylation and renders the nerve agent-acetylcholinesterase complex highly resistant to regeneration by any known antidote. Slower aging by VX suggests it should be possible to develop more effective antidotes and treatments. The reaction products of acetylcholinesterase with VX before and after the "aging" reaction were solved near atomic resolution by X-ray crystallography to aid in antidote development.
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This reaction is identical to the normal benzilic acid rearrangement, except that an alkoxide or an amide anion is used in place of a hydroxide ion. The alkoxide used should not be easily oxidizable (such as potassium ethoxide) as this favors the Meerwein–Ponndorf–Verley reduction pathway as a side reaction. The reaction is second order overall in terms of rate, being first order in terms of alkoxide and first order in terms of diketone. The product of the reaction is an α-hydroxy–ester or an α-hydroxy-amide.
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Carbene dimerization is a type of organic reaction in which two carbene or carbenoid precursors react in a formal dimerization to an alkene. This reaction is often considered an unwanted side-reaction but it is also investigated as a synthetic tool. In this reaction type either the two carbenic intermediates react or a carbenic intermediate reacts with a carbene precursor. An early pioneer was Christoph Grundmann reporting on a carbene dimerisation in 1938.Grundmann, C. (1938), Über die Zersetzung der Diazoketone. Justus Liebigs Annalen der Chemie, 536: 29–36.
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Beyond this synthetic application, protodeboronation was rarely noted or valued in other chemical processes throughout the early 20th century. However, in more recent years, protodeboronation has emerged as a problematic side reaction with many chemical processes that utilise boronic acids. In particular, boronic acids have become increasingly important reagents for the facile construction of carbon-carbon and carbon-heteroatom bonds via metal-catalysed cross-coupling reactions. This has resulted in an increased usage of boronic acids, and subsequently followed by an increased number of reports concerning problematic protodeboronation.
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A common side reaction taking place with SN2 reactions is E2 elimination: the incoming anion can act as a base rather than as a nucleophile, abstracting a proton and leading to formation of the alkene. This pathway is favored with sterically hindered nucleophiles. Elimination reactions are usually favoured at elevated temperatures because of increased entropy. This effect can be demonstrated in the gas-phase reaction between a sulfonate and a simple alkyl bromide taking place inside a mass spectrometer:Gas Phase Studies of the Competition between Substitution and Elimination Reactions Scott Gronert Acc. Chem. Res.
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Unwanted side reactions such as threonine and asparagine production can occur if a buildup of intermediates occurs, so scientists have developed mutant strains of C. glutamicum through PCR engineering and chemical knockouts to ensure production of side-reaction enzymes are limited. Many genetic manipulations conducted in industry are by traditional cross-over methods or inhibition of transcriptional activators. Expression of functionally active human epidermal growth factor has been brought about in C. glutamicum, thus demonstrating a potential for industrial-scale production of human proteins. Expressed proteins can be targeted for secretion through either the general secretory pathway or the twin-arginine translocation pathway.
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Catalytic reforming is a chemical process used to convert petroleum refinery naphthas distilled from crude oil (typically having low octane ratings) into high-octane liquid products called reformates, which are premium blending stocks for high-octane gasoline. The process converts low-octane linear hydrocarbons (paraffins) into branched alkanes (isoparaffins) and cyclic naphthenes, which are then partially dehydrogenated to produce high-octane aromatic hydrocarbons. The dehydrogenation also produces significant amounts of byproduct hydrogen gas, which is fed into other refinery processes such as hydrocracking. A side reaction is hydrogenolysis, which produces light hydrocarbons of lower value, such as methane, ethane, propane and butanes.
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Toluene derivatives with heteroatom-containing substituents in the ortho position undergo site-selective benzylic lithiation in the presence of organolithium compounds (either alkyllithiums or lithium dialkylamides). Coordination of the Lewis acidic lithium atom to the Lewis basic heteroatom, as well as inductive effects derived from the electronegativity of the heteroatom, encourage selective deprotonation at the benzylic position. Competitive ring metalation (directed ortho-metalation) is an important side reaction, but a judicious choice of base often allows for selective benzylic metalation. Useful heteroatom-containing directing groups include dialkylamines,Jones, F. N.; Zinn, M. F.; Hauser, C. R. J. Org. Chem.
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Concentrated sulfuric acid dehydrates n-butyl alcohol to yield 1-butene, which reacts with phthalic anhydride to produce n-butyl phthalate. Phthalic anhydride does react directly with 1-butanol to form this same intermediate, but further reaction to form dibutyl phthalate does occur to a significant extent. Carrying out the procedure using 1-butene avoids this side reaction. Monobutyl phthalate is isolated and then added to a mixture of benzyl bromide in acetone in the presence of potassium carbonate (to keep the pH high to facilitate the substitution reaction required to form the second ester linkage), from which BBP can then be isolated.
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Association and dissociation of a phosphine ligand also occurs in the case of Grubbs catalysts.Ansyln, E. V.; Dougherty, D. A. Organotransition Metal Reaction Mechanisms and Catalysts. Modern Physical Organic Chemistry, Murdzek, J., Ed. University Science Books, 2006, pp. 745-746. In an RCM reaction, the alkylidene undergoes an intramolecular [2+2] cycloaddition with the second reactive terminal alkene on the same molecule, rather than an intermolecular addition of a second molecule of starting material, a common competing side reaction which may lead to polymerizationLee, C. W.; Grubbs, R. H. (2001). “Formation of Macrocycles via Ring-Closing Olefin Metathesis”.
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PTFE is produced by free-radical polymerization of tetrafluoroethylene. The net equation is : n F2C=CF2 → −(F2C−CF2)n− Because tetrafluoroethylene can explosively decompose to tetrafluoromethane and carbon, special apparatus is required for the polymerization to prevent hot spots that might initiate this dangerous side reaction. The process is typically initiated with persulfate, which homolyzes to generate sulfate radicals: :[O3SO−OSO3]2− ⇌ 2 SO4•− The resulting polymer is terminated with sulfate ester groups, which can be hydrolyzed to give OH end-groups.Carlson, D. Peter and Schmiegel, Walter (2000) "Fluoropolymers, Organic" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim.
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As mentioned above, aryl and alkenyl nonaflates are useful as electrophiles in palladium catalyzed cross coupling reactions. Their reactivity generally mirrors that of the more commonly encountered triflate electrophiles, but nonaflates tend to be less prone to hydrolysis to ketones (in the case of alkenyl sulfonates) and phenols (in the case of aryl sulfonates). Their resistance to hydrolysis makes nonaflates superior electrophiles in Buchwald-Hartwig couplings, where this side reaction can be deleterious to yields of the desired product. The sodium enolates of β-ketoesters react with 1.15 equivalents of NfF to give the corresponding alkenyl nonaflates in high yield.
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The model-independent evidence is compatible with a wide set of scenarios regarding the nature of the dark matter candidate and related astrophysical, nuclear and particle physics, for example: neutralinos, inelastic dark matter, self-interacting dark matter, and heavy 4th generation neutrinos, A careful quantitative investigation of possible sources of systematic and side reactions has been regularly carried out and published at the time of each data release. No systematic effect or side reaction able to account for the observed modulation amplitude and to simultaneously satisfy all the requirements of the signature has been found. The experiment has also obtained and published many results on other processes and approaches.
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For example, oxidation of cyclohexane into cyclohexanol and cyclohexanone and ortho-xylene into phthalic anhydride have led to catastrophic explosions when reaction control failed. Thermal runaway may result from unwanted exothermic side reaction(s) that begin at higher temperatures, following an initial accidental overheating of the reaction mixture. This scenario was behind the Seveso disaster, where thermal runaway heated a reaction to temperatures such that in addition to the intended 2,4,5-trichlorophenol, poisonous 2,3,7,8-tetrachlorodibenzo-p-dioxin was also produced, and was vented into the environment after the reactor's rupture disk burst. Thermal runaway is most often caused by failure of the reactor vessel's cooling system.
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Toluene hydrodealkylation converts toluene to benzene. In this hydrogen-intensive process, toluene is mixed with hydrogen, then passed over a chromium, molybdenum, or platinum oxide catalyst at 500–650 °C and 20–60 atm pressure. Sometimes, higher temperatures are used instead of a catalyst (at the similar reaction condition). Under these conditions, toluene undergoes dealkylation to benzene and methane: :C6H5CH3 \+ H2 → C6H6 \+ CH4 This irreversible reaction is accompanied by an equilibrium side reaction that produces biphenyl (aka diphenyl) at higher temperature: :2 + If the raw material stream contains much non-aromatic components (paraffins or naphthenes), those are likely decomposed to lower hydrocarbons such as methane, which increases the consumption of hydrogen.
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The vinylsulfone group reacts with the nucleophilic functional groups of the fibers by Michael addition to form a covalent ether bond: > Reaktion der Vinylsulfon-Verbindungen mit den Hydroxylgruppen der Cellulose > Reaction of vinyl sulfone compounds with hydroxyl groups of cellulose (HO- > CELL) An unfavorable side reaction in the dyeing process is the conversion of the vinylsulfone group to the 2-(hydroxy)ethylsulfonyl group:Die Reaktion der VS- Reaktivfarbstoffe mit Wasser wird in der Literatur auch als "Hydrolyse" bezeichnet, siehe: > Reaktion der Vinylsulfon-Verbindungen mit Wasser/OH− als unerwünschte > Nebenreaktion beim Färben > Reaction of vinylsulfone compounds with water/OH− during dying The hydroxylated, unreactive dye has to be washed out during the post- treatment.
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In this case, water produced along with the acetal product is destroyed when it hydrolyses residual orthoester molecules, and this side reaction also produces more alcohol to be used in the main reaction. Acetals are used as protecting groups for carbonyl groups in organic synthesis because they are stable with respect to hydrolysis by bases and with respect to many oxidizing and reducing agents. They can either protect the carbonyl in a molecule (by temporarily reacting it with an alcohol) or a diol (by temporarily reacting it with a carbonyl). That is, either the carbonyl, or the alcohols, or both could be part of the molecule whose reactivity is to be controlled.
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First, in the case of the diaryl system 9, relatively high stereoselectively is achieved despite the isosteric nature of the ketone substituents, suggesting that electronics in addition to sterics may play a role in the stereoselectivity of the CBS reduction. Differences in the substitution of the alkyne moieties in ynones 11 and 12 result in a change of selectivity for the alkyne to function as the more sterically bulky substituent rather than the smaller one. For the α,β unsaturated systems 10-12, efficient reduction of the ketone occurs despite the possible side reaction of hydroboration of the C-C unsaturated bond. The CBS reduction has also been shown to tolerate the presence of heteroatoms as in ketone 13, which is capable of coordinating to the borane.
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A small fraction of electrons leave the electron transport chain before reaching complex IV. Premature electron leakage to oxygen results in the formation of superoxide. The relevance of this otherwise minor side reaction is that superoxide and other reactive oxygen species are highly toxic and are thought to play a role in several pathologies, as well as aging (the free radical theory of aging). Electron leakage occurs mainly at the Qo site and is stimulated by antimycin A. Antimycin A locks the b hemes in the reduced state by preventing their re- oxidation at the Qi site, which, in turn, causes the steady-state concentrations of the Qo semiquinone to rise, the latter species reacting with oxygen to form superoxide. The effect of high membrane potential is thought to have a similar effect.
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A metal acetylide is formed in situ when an alkyne is treated with a strong bases such as a hydroxide or an alkoxide: # HC≡CH + KOH HC≡CK + H2O # RR'C=O + HC≡CK RR'C(OK)C≡CH The metal acetylide then reacts with an aldehyde or ketone to form a propargyl alcohol. When an α-hydrogen is present (as is the case when the carbonyl is an aldehyde), it will tautomerize to the corresponding enone. The applicable substrates that undergo a Favorskii reaction are limited when compared to the conventional reaction because using an excess of hydroxide base introduces aldol condensation as a more significant competing side reaction. Since enolates do not react with acetylene, the reaction can be often be a poor substitute for the conventional reaction, especially when reaction is used on aldehydes.
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Oxidation can occur both at sulfur, giving a thiophene S-oxide, as well as at the 2,3-double bond, giving the thiophene 2,3-epoxide, followed by subsequent NIH shift rearrangement. Oxidation of thiophene by trifluoroperacetic acid also demonstrates both reaction pathways. The major pathway forms the S-oxide as an intermediate, which undergoes subsequent Diels-Alder-type dimerisation and further oxidation, forming a mixture of sulfoxide and sulfone products with a combined yield of 83% (based on NMR evidence): 500px In the minor reaction pathway, a Prilezhaev epoxidation results in the formation of thiophene-2,3-epoxide that rapidly rearranges to the isomer thiophene-2-one. Trapping experiments demonstrate that this pathway is not a side reaction from the S-oxide intermediate, while isotopic labeling with deuterium confirm that a 1,2-hydride shift occurs and thus that a cationic intermediate is involved.
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Photocatalysts must confirm to several key principles in order to be considered effective at water splitting. A key principle is that and evolution should occur in a stoichiometric 2:1 ratio; significant deviation could be due to a flaw in the experimental setup and/or a side reaction, neither of which indicate a reliable photocatalyst for water splitting. The prime measure of photocatalyst effectiveness is quantum yield (QY), which is: : QY (%) = (Photochemical reaction rate) / (Photon absorption rate) × 100% This quantity is a reliable determination of how effective a photocatalyst is; however, it can be misleading due to varying experimental conditions. To assist in comparison, the rate of gas evolution can also be used; this method is more problematic on its own because it is not normalized, but it can be useful for a rough comparison and is consistently reported in the literature.
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The so-called Jones reagent is prepared by dissolving chromium trioxide (CrO3) in aqueous sulfuric acid, which results in formation of a reddish solution containing chromic acid (H2CrO4) and oligomers thereof. Addition of Jones reagent to a solution of a primary alcohol in acetone (as first described by Jones ) results in oxidation of the alcohol to a carboxylic acid. This classical protocol, involving a direct addition, is used very often regardless of the fact that it frequently leads to the formation of substantial amounts of esters (possessing the structure R-CO-O- CH2-R) derived from oxidative dimerization of primary alcohols. Holland and Gilman proved that this side reaction can be greatly suppressed by following the inverse addition protocol whereby a solution of the primary alcohol in acetone is slowly added to Jones reagent under conditions as dilute as practical.
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The stereochemical consequences of a concerted reaction pathway on the reaction outcome suggested an experiment where one would correlate the obtained reaction stereochemistry with the predicted reaction stereochemistry for a model substrate. Observing the formation of ai- and sr-cyclopentene products would support the notion that a stepwise, non-concerted mechanism is operative whereas their absence would point towards a fully concerted mechanism. As it turned out finding an appropriate substituted model substrate to study the stereochemical outcome of the vinylcyclopropane rearrangement was much more challenging than initially thought since side reaction such as the homodienyl 1,5]-hydrogen shifts and more so thermal stereomutations tend to scramble stereochemical distinctions much faster than rearrangements lead to the cyclopentene products. Stereomutations Even though deconvolution of the complex kinetic scenarios underlying these rearrangements was difficult there have been several studies reported where exact and explicit deconvolutions of kinetic and stereochemical raw data to account for the stereochemical contributions arising from competitive stereomutations was possible.
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